1. Field of the Invention
The present invention relates to a satellite broadcasting receiving converter which can receive radio waves transmitted from a plurality of neighboring satellites.
2. Description of the Related Art
In receiving radio waves from a plurality of neighboring satellites, that is, when satellite broadcasting signals having leftward circularly polarization and rightward circularly polarization are respectively transmitted from two satellites and these satellite broadcasting signals are inputted to separate feed horns and waveguides and received by one LNB, for example, it is necessary to perform frequency conversion of the leftward circularly polarized signal and the rightward circularly polarized signal which are picked up by the waveguides into intermediate frequency bands which are different from each other. In this case, the leftward circularly polarized signal and the rightward circularly polarized signal transmitted from one satellite are subjected to frequency conversion into the different intermediate frequency bands using two mixers. Here, among four mixers served for two satellites, by connecting a first oscillator to two mixers for leftward circularly polarization and by connecting the second oscillator to two mixers for rightward circularly polarization, it is possible to perform frequency conversion of the left ward circularly polarized signal and the rightward circularly polarized signal respectively transmitted from two satellites into the intermediate frequency bands using the first oscillator and the second oscillator which differ in oscillation frequency.
To design a layout of such a converter circuit on a printed circuit board, it is inevitably necessary to make portions of oscillation signal lines which connect between the first and second oscillators and respective mixers cross intermediate frequency signal lines for intermediate frequency signals outputted from respective mixers. For example, assume a case in which the converter circuit is designed such that the first and second oscillators are sandwiched by the leftward and rightward circularly polarized signal lines of two satellites, respective leftward circularly polarized signal lines are arranged at the inside, and respective rightward circularly polarized signal lines are arranged at the outside. In this case, to connect the second oscillator to two mixers for rightward circularly polarization positioned at the outside, it is necessary to make the oscillation signal lines cross respective intermediate frequency signal lines. Accordingly, conventionally, the converter is mounted on a front surface of the printed circuit board which has a ground pattern on a back surface thereof, and at portions where the oscillation signal lines cross the intermediate frequency signal lines, both ends of each coaxial cable mounted on the back surface of the printed circuit board are made to penetrate the printed circuit board and are soldered to the oscillation signal lines so that the oscillation signal lines are made to cross the intermediate frequency signal lines by way of the coaxial cables mounted on the back surface side of the printed circuit board.
Further, with respect to the satellite broadcasting receiving converter for receiving radio waves transmitted from a plurality of neighboring satellites, for example, when a degree of elongation between two satellites launched to the sky is small and the radio waves transmitted from these two satellites are received by one outdoor antenna device installed on the ground, it is necessary to mount two waveguides on the outdoor antenna device such that the waveguides face a reflector.
Conventionally, as an example of such a two-satellite broadcasting receiving converter, there has been known a converter which uses two waveguides having the same structure for one satellite and mounts these waveguides such that the waveguides are arranged in parallel and face a reflector in an opposed manner. In this case, opening end faces of two waveguides which are arranged in parallel are positioned on the same plane so that radio waves which are transmitted from two satellites having a given degree of elongation are respectively incident on the inside of the converter from the opening ends of two waveguides after being reflected by the reflector.
Further, as another conventional example of such a two-satellite broadcasting receiving converter, there has been known a converter in which two waveguides are integrally formed by diecasting using alloy of aluminum, zinc or the like and these waveguides are arranged to face a reflector in a state that the waveguides or openings of the waveguides are inclined. In this case, respective opening end faces of two waveguides are positioned within different planes having a V shape so that radio waves transmitted from two satellites having a given degree of elongation are incident on the inside of the converter in the direction perpendicular to opening end faces of the two waveguides after being reflected on the reflector.
As mentioned previously, according to a related art in which when the broadcasting signals transmitted from a plurality of satellites are received by one LNB, the oscillation signal lines and the intermediate frequency signal lines are made to cross each other using the coaxial cables, since respective signal lines are grounded, the interference between signals having different frequencies can be reduced. However, it is necessary to provide the coaxial cables in addition to the printed circuit board and the coaxial cables must be soldered to the signal lines after projecting the coaxial cables from the back surface to the front surface of the printed circuit board and hence, the step for connecting the coaxial cables is time-consuming and cumbersome and it gives rise to a problem that the manufacturing cost is pushed up.
Further, with respect to the above-mentioned related arts, in the former type which arranges two waveguides in parallel, the waveguide for one satellite can be directly utilized as waveguides for two satellites and hence, it is possible to have an advantageous effect that the elevation of the manufacturing cost can be suppressed due to the common use of parts. However, since the opening end faces of two waveguides which are arranged in parallel are positioned within the same plane, when the radio waves transmitted from two satellites having given degree of elongation enter respective waveguides after being reflected on a common reflector, portions of the reflector which reflect only the radio waves transmitted from one satellite are increased thus giving rise to a problem that it is inevitably necessary to use a large-sized reflector.
To the contrary, in the latter type in which two waveguides are inclined, since a preset angle which is preliminarily set to a desired angle is provided to the opening end faces of two waveguides, the radio waves transmitted from two satellites enter respective waveguides after being reflected on a common portion of the reflector and hence, it is possible to use a small-sized or miniaturized reflector correspondingly. However, since a mold for diecasting which has a complicated structure and is expensive is necessary for integrally forming two waveguides and hence, there arises a problem that the manufacturing cost of the satellite broadcasting receiving converter is pushed up. Further, it is necessary to change the inclination angles of two waveguides corresponding to the degree of elongation of the satellites which are subjected to signal reception so that there has been a problem that the latter type cannot provide versatility.